1. Field of the Invention
The present invention relates to a rotor for a dynamo-electric machine including magnetic bodies disposed between adjacent claw-shaped magnetic poles for minimizing magnetic flux leakage between the claw-shaped magnetic poles, and to a method for magnetizing the magnetic bodies.
2. Description of the Related Art
FIG. 9 is a cross-section of a conventional automotive alternator, FIG. 10 is a perspective of the rotor in FIG. 9, and FIG. 11 is an exploded view of the rotor in FIG. 10. This automotive alternator includes: a case 3 comprising an aluminum front bracket 1 and an aluminum rear bracket 2; a shaft 6 disposed in the case 3 to one end of which a pulley 4 is secured; a Lundell-type rotor 7 secured to the shaft 6; fans 5 secured to both ends of the rotor 7; a stator 8 secured to the inner wall of the case 3; slip rings 9 secured to the other end of the shaft 6 for supplying electric current to the rotor 7; a pair of brushes 10 moving in contact with the slip rings 9; a brush holder 11 accommodating the brushes 10; a rectifier 12 in electrical contact with the stator 8 for converting an alternating current generated in the stator 8 to a direct current; a heat sink 17 fitted over the brush holder 11; and a regulator 18 attached to the heat sink with adhesive for adjusting the magnitude of the alternating current generated in the stator 8.
The rotor 7 includes: a rotor coil 13 having wire 31 wound onto a bobbin 30 for generating magnetic flux by passing an electric current through the wire 31; and a pole core 14 disposed so as to cover the rotor coil 13 in which magnetic poles are produced by the magnetic flux generated by the rotor coil 13. The pole core 14 includes a first pole core body 21 and a second pole core body 22 which mutually intermesh. The first pole core body 21 is formed with a plurality of first claw-shaped magnetic poles 23 evenly spaced around a circumferential portion thereof. Like the first pole core body 21, the second pole core body 22 is made of iron and is formed with a plurality of second claw-shaped magnetic poles 24 evenly spaced around a circumferential portion thereof. A magnetic body 33 magnetized in directions which reduce magnetic flux leakage between the claw-shaped magnetic poles 23, 24 is inserted between the mutually intermeshing first claw-shaped magnetic poles 23 and second claw-shaped magnetic poles 24. The magnetic body 33 is shaped so as to wind in a zigzag circumferentially, and is composed of plastic magnets.
The stator 8 includes: a stator core 15; and a stator coil 16 composed of wire wound into the stator core 15 in which an alternating current is generated by changes in the magnetic flux arising in the rotor coil 13 as the rotor 7 rotates.
In an automotive alternator of the above construction, a current is supplied from a battery (not shown) via the brushes 10 and the slip rings 9 to the rotor coil 13, generating magnetic flux, and the first claw-shaped magnetic poles 23 in the first pole core body 21 are magnetized with a north-seeking (N.) pole, and the second claw-shaped magnetic poles 24 in the second pole core body 22 are magnetized with a south-seeking (S.) pole. At the same time, because the pulley 4 is driven by the engine and the rotor 7 is rotated by the shaft 6, a rotating magnetic field is imparted to the stator coil 16 and electromotive force arises in the stator coil 16. This alternating-current electromotive force is converted to a direct current by means of the rectifier 12, its magnitude is regulated by the regulator 18, and the battery is recharged.
In a conventional rotor 7 for an automotive alternator, because centrifugal force acts on the first and second claw-shaped magnetic poles 23, 24 as the rotor 7 rotates making the first and second claw-shaped magnetic poles 23, 24 vibrate in the direction of arrow A in FIG. 12, one problem has been that there is a risk that the magnetic body 33 will be damaged in places where the tips of the claw-shaped magnetic poles collide therewith, and damage actually occurs when the rotational frequency of the rotor 7 is approximately 10000 to 15000 rpm, for example.
In order to prevent such damage to the magnetic body 33, the magnetic body can be secured to the first pole core body 21 and the second pole core body 22 with adhesive, but even then, one problem has been that the magnetic body 33 is simultaneously subjected to loads of different magnitude and direction from each of the claw-shaped magnetic poles 23, 24 during rotation of the rotor 7 and there is still a risk that the magnetic body 33 will be damaged.